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Noise reduction for IVA

SteveWallace - 23/3/14 at 12:39 PM

Having got my exhaust system back the other day, I decided to test it for noise using an i-phone app. First attempt the car wouldn't run properly at all - minor panic - then realised that I had ran out of petrol (doh). Trip to garage with petrol can and then tried again and got 101db, so two over the IVA limit of 99db. Not sure of the accuracy of the app, but don't want to risk it.

I need to check what the exhaust maker put in the can, if anything, but assuming that it wasn't a lot, do people think that some Acousta-fil will get the noise down to where it needs to be, or is something more radical needed. I'm kind of surprised at the noise level given the size of the can.

Description

P.S. I had my CD of photos back in the post from VOSA yesterday, so I guess that I'm not far away from being offered a test date.

rusty nuts - 23/3/14 at 12:44 PM

Did you do the test in an open area without any buildings near? Doing the test in a driveway etc could possibly give a false reading. Also might be worth checking induction noise.

Kev99 - 23/3/14 at 01:56 PM

If your worried about the noise u can always use a db killer for IVA loads of diff types etc

will kill the power but its IVA it will fall out on way home

Kev......

SteveWallace - 23/3/14 at 02:16 PM

quote:
Originally posted by rusty nuts
Did you do the test in an open area without any buildings near? Doing the test in a driveway etc could possibly give a false reading. Also might be worth checking induction noise.

That's a good point, I did it in a bit of a hurry just to see and it was within a couple of feet of the open garage and I didn't put the bonnet on. I have limited scope to move it without being illegal, but I can probably get a couple of car lengths away and put the bonnet on to see what difference I get. The IVA tester will be in a much more open space, so there will be a margin for error.

I did think about a db killer, but I don't want to drill a hole in my shiny new exhaust to put the locking bolt through and I'm not convinced that the IVA tester will not just fail me on the basis that he knows that its going to fall out two minutes after the test.

snapper - 23/3/14 at 03:07 PM

Db killer between 4 branch and pipe to can will reduce to about 96Db

40inches - 23/3/14 at 03:18 PM

quote:
Originally posted by SteveWallace

quote:
Originally posted by rusty nuts
Did you do the test in an open area without any buildings near? Doing the test in a driveway etc could possibly give a false reading. Also might be worth checking induction noise.

That's a good point, I did it in a bit of a hurry just to see and it was within a couple of feet of the open garage and I didn't put the bonnet on. I have limited scope to move it without being illegal, but I can probably get a couple of car lengths away and put the bonnet on to see what difference I get. The IVA tester will be in a much more open space, so there will be a margin for error.

I did think about a db killer, but I don't want to drill a hole in my shiny new exhaust to put the locking bolt through and I'm not convinced that the IVA tester will not just fail me on the basis that he knows that its going to fall out two minutes after the test.

You will not find any IVA testers as eager for you to get a pass as those at Notttingham.
My noise test failed initially at around 100db, I had a Decibel Killer in the box of bits in the trailer, so he told me to fit it.
It passed at 98db with more than a bit of leeway from the tester

It also "failed" on the edge radius on the silencer, he told me to take the MK back to the car park, wait until the silencer had cooled down and fit some rubber edge trim. He came up to the car park, checked that the trim was in place and handed over the pass certificate

As he explained to me, it wasn't his job to second guess what happened on the way back home, and more than a few have changed steering wheels in the car park. Not his problem.
Fitting a db killer initially may alter the emissions.The examiner also needs to fit the probe into the silencer, may not be possible with a db killer fitted.

adithorp - 23/3/14 at 06:22 PM

quote:
Originally posted by SteveWallace
I did think about a db killer, but I don't want to drill a hole in my shiny new exhaust to put the locking bolt through and I'm not convinced that the IVA tester will not just fail me on the basis that he knows that its going to fall out two minutes after the test.

The tester has to pass it if the level is OK. What happens latter is of no interest to him... unless it comes back for retest in a different state than the original test the he has the ability to retest those items even if they passed first time.

Did you do the test at the test at the correct distance/angle? A hole drilled on the underside of the exhaust will hardly be noticeable. Some sort of sound deadening on the inside inside of the bonnet will reduce some induction/engine noise... every little helps.

rusty nuts - 23/3/14 at 06:53 PM

A hole drilled on the underside of the exhaust will hardly be noticeable. .

Often the cause of failing the emissions test due to high lambda reading

adithorp - 23/3/14 at 07:09 PM

quote:
Originally posted by rusty nuts
A hole drilled on the underside of the exhaust will hardly be noticeable. .

Often the cause of failing the emissions test due to high lambda reading

I meant at the tip to secure a Db killer. The emission probe should be a lot further in than that... and there'd be a screw in/blocking it anyway.

SteveWallace - 23/3/14 at 08:14 PM

quote:
Originally posted by snapper
Db killer between 4 branch and pipe to can will reduce to about 96Db

All of the ones that I've seen fit on the tail pipe. Are you saying that you can get them to fit further up stream? Not sure that I can get one to fit the tail pipe as its a rolled end and turns through nearly 90 degrees.

The Black Flash - 23/3/14 at 10:54 PM

Currently having major trouble with this myself and have tried all sorts.
Anyway I've tried a load of different things and tested with a cheap sound meter (most phone ones aren't accurate up around 100db from what I've read, due to the microphone). db killers and various home made devices in various positions etc. They will take a few db off but there seems to be a limit to what you can achieve with them. I've got down to just under 98 on my meter but adding more and more baffles don't take it any lower, even to the point that it's so restricted that exhaust starts leaking out of the silencer seams!
Things in the end of the pipe seem to have more effect than things further upstream towards the engine. Bear in mind though that it's a fail if he can't get his emissions probe up the end, if he still needs to.

After all the tests, the most effect I've had was the simplest; a washer with a 20mm hole in the end, two 1" steel legs welded on, and popped into the end of the pipe:

That's had as much effect as anything else I've tried, and easily inserted and removed.

SteveWallace - 24/3/14 at 12:34 PM

That's not a bad idea, but, as you say, I'll only be able to fit it once he's done the emissions test. I don't want to have to rely on the grace and favour of the tester to allow me to do this between the emissions test and the noise test, but I'll make one up as a backup plan.

I think that my first fix is going to be to try Acousta-fil.

I've put a post in the 'wanted' section to see if anyone in the Nottingham/derby area has a proper db meter that I could borrow as I've started not to trust my app.

BenB - 24/3/14 at 12:56 PM

At my SVA test my rev counter was under-reading by about 20%. I only realised afterwards Of course having twin pipes it means the dBs are coming out of both sides and they only measure on one side so it was never going to be a problem even with a straight through pipe with the restrictors chopped off.

SteveWallace - 24/3/14 at 01:50 PM

quote:
Originally posted by The Black Flash

After all the tests, the most effect I've had was the simplest; a washer with a 20mm hole in the end, two 1" steel legs welded on, and popped into the end of the pipe:

That's had as much effect as anything else I've tried, and easily inserted and removed.

Not sure how effective it would be, but I guess that I could make one of these up and bolt it to the perforated tube that runs down the inside of the silencer, just far enough back so that the IVA man could get his probe in. Anyone know how far in it needs to go?

adithorp - 24/3/14 at 01:59 PM

The emisions probe would still go in through that plate.

Ba careful with accousta-fill as the on-line amount calculator is thought by many to cause overpacking and so not enough silencing.

SteveWallace - 24/3/14 at 05:33 PM

I know what you mean. I tried a few of the on line calculators and got answers that varied by a factor of two. I've gone for the lower amount as there seemed to be more at this end of the range.

I don't weld so I'm also going to cut a couple of baffles as shown in The Black Flash's photo with different sized holes and see what happens. I'll do them in thin aluminium first and just push fit and then convert to mild steel with a small bolt fit if I find a size that works.

[Edited on 24/3/14 by SteveWallace]

The Black Flash - 24/3/14 at 08:44 PM

quote:
Originally posted by adithorp
The emisions probe would still go in through that plate.

Yeah sorry should have said, the probe goes through that (or pushes it further up), either way, the tester didn't complain.

SteveWallace - 28/3/14 at 05:37 PM

quote:
Originally posted by The Black Flash

After all the tests, the most effect I've had was the simplest; a washer with a 20mm hole in the end, two 1" steel legs welded on, and popped into the end of the pipe:

That's had as much effect as anything else I've tried, and easily inserted and removed.

I made something up that looks similar using some scrap aluminium except that I drilled four 13mm diameter holes in it as it was easer than making one big one. Tested it today and got the noise down to 98-99db, so I think that I'm there as long as the I-phone app is not reading too low. I'll make it up properly in steel over the weekend so that it at least looks like its going to stay in. I'm also going to repack the can with Acousta-fil tomorrow to knock it down a bit more to give me a margin for error.

Thanks for the suggestion Black Fish.

IVA date confirmed as Friday 4th April, so the usual picture heavy post to follow in a couple of days.

The Black Flash - 29/3/14 at 01:46 PM

quote:
Originally posted by SteveWallace

quote:
Originally posted by snapper
Db killer between 4 branch and pipe to can will reduce to about 96Db

All of the ones that I've seen fit on the tail pipe. Are you saying that you can get them to fit further up stream? Not sure that I can get one to fit the tail pipe as its a rolled end and turns through nearly 90 degrees.

You can fit them anywhere they'll go, so yes you can put it before the can or inside it. It seemed to me that it was less effective than being in the end, but as you say often there's no choice.